3.1. Introduction

Honey bees
produce airborne volatile organic compounds which serve as indicators of the
‘status’ of the colony. As such, the collection, analyses, bioactivity of
identified honey bee odours is vital to understanding how social cohesion is
maintained, regulated and influenced by various biotic factors such as foreign
intruders (Torto et al., 2005, 2007a,
2007b) and pathogens (Swanson et al.,
2009). Odours associated with honey bees have been used to improve colony
vigour and to manage certain pest such as the small hive beetle Aethina tumida, (Teal et al., 2006; Arbogast et al., 2007; Torto et al., 2007b).

A
specialized method that provides information on honey bee detection and
sensitivity to specific compounds is coupled Gas Chromatography-ElectroAntennographic
Detection (GC-EAD) (Schneider, 1957; Baker et
al., 1985; Torto et al., 2007a;
Swanson et al. 2009). This coupled
system uses an insect antenna in tandem with a flame ionization detector (FID)
to link the electrical activity stemming from neurons signalling receptor
binding of chemicals to individual peaks.GC-EAD is an excellent analytical tool
but works best for chemicals detected by many receptors thereby producing a
strong electrical stimulation from the antenna. In this hybrid method,
volatiles emerging from a GC column are split between a conventional GC
detector (chemical sensor) and an antenna mounted between two electrodes
(biological sensor). The interpretation of detected compounds requires an
understanding of insect physiology, since antennal stimulation to chemicals
represents activity which may indicate attraction or repellence. Some chemicals
may be detected by a single receptor, transmitted by a single neuron and then
amplified in the brain while others may stimulate several receptors and their
associated receptor neurones. Honey bee chemosensory organs can be much more
sensitive to bioactive compounds than analytical detectors, sometimes leading
to strong electrophysiological responses to correspondingly weak chemically
(FID) detected components. Although the honey bee antenna is most commonly
used, other body parts having chemosensory activity can be used as biosensors.
Antennae and body parts with weak electrophysiological activity can have their
activity amplified by mounting multiple parallel sensory organs in tandem
across a single electrode.

This
section focuses on methods to collect honey bee odours outside of the colony
environment (ex-situ volatile
collection) and to carry out electrophysiological recordings using antenna or
other chemosensory body parts of the honey bee.